The genetic, molecular, and biochemical causes of mood disorders are still poorly understood. Disturbances in the limbic-hypothalamic- pituitary-adrenal (LHPA) stress axis and the serotonin system are commonly found in depression. However, the pathophysiology of mood disorders and the effectiveness (or lack thereof) of various antidepressants suggest that other neural systems may contribute to the primary or secondary changes in this disorder. The availability of brains from control and depressed subjects provides us with the opportunity to examine the molecular changes in depression in the context of known circuits. As described in the Center Overview, we will address the central hypothesis using two major approaches to the study of alterations in gene expression: 1) The "expression candidate approach" will rely on classical tools such as in situ hybridization to characterize known gene products in the context of circuits proposed to be involved in the regulation of stress emotional responsiveness and emotional executive function. It will also include preliminary genetic characterization of the DNA from control and depressed subjects for markers with known polymorphisms relevant to psychiatric diseases (i.e. serotonin transporter) (Specific Aim I). 2) The "expression array approach" will rely on the new microarray and DNA chip technologies to screen for known and unknown genes whose expression may be altered (either induced or repressed) in depression (see Dr. Cox's proposal). The opportunity to scan the expression levels of thousands of mRNA species for regulatory changes in important brain regions will clearly enhance our understanding of both stress and monoamine systems, and will also identify regulated genes in new neural pathways that are relevant to mood disorders. We may also detect highly regulated mRNA sequences from genes with unidentified functions, leading to new areas of study. The post-array analyses will include studies for validation of the regulation changes detected by microarray and DNA chip technologies using additional control and depressed brains. Validation studies will include comparison of mRNA values (and ratios) with those obtained via in situ hybridization of known mRNAs. Biological validation will include in situ hybridization analysis to identify the anatomical sties of expression of altered mRNAs and regulatory studies with rodent models (Specific Aim II). This work will rely on the effects of the Stanford site, and will integrate with the findings from UC site, in order to yield a more comprehensive view of the biological underpinnings of major depressive disorders.